1. Field of the Invention
This invention generally relates to semiconductor manufacturing equipment and, more particularly, to a system and method for rapid thermal processing of a semiconductor wafer.
2. Related Art
To make semiconductor devices of decreased dimensions, new processing and manufacturing techniques have had to be developed. One important requirement for the new techniques is to be able to reduce the amount of time that a semiconductor wafer is exposed to high temperatures during processing. One such processing technique designed to address this requirement is known as Rapid Thermal Processing (RTP). The rapid thermal processing technique, typically includes quickly raising the temperature of the wafer and holding it at that temperature for a time long enough to successfully perform a fabrication process, while avoiding such problems as unwanted dopant diffusion that would otherwise occur at the high processing temperatures.
Generally, conventional RTP systems use a light source and reflectors to heat the bulk of the semiconductor wafer. The light source is usually a bank of Halogen lamps that emit radiation energy that is focused on the wafer by the reflectors.
Conventional Halogen lamp-based RTP systems have considerable drawbacks with regard to achieving and maintaining a uniform temperature distribution across the active layer of the wafer surface. For example, the Halogen lamp has a filament, which generates broadband radiation. By applying more power to the filament, the intensity of the lamp can be increased. However, silicon wafers are heated using a useable band of short wavelengths, and are otherwise transparent to wavelengths outside of this band. The radiation from the lamp remains mostly outside of the useable wavelength band during typical halogen lamp operation. As a consequence, much of the applied power is wasted.
Another drawback to filament type lamps is that they generally create a broad wavelength distribution that is independently uncontrollable. Consequently, temperature fluctuations occur on the surface of the wafer which may cause crystal defects and slip dislocations in the wafer at high temperatures (e.g. xcx9c1000xc2x0 C.) and under various lamp configurations.
One particular solution to the drawbacks of Halogen lamp-based systems is disclosed in U.S. Pat. No. 5,893,952. In the ""952 patent, an apparatus is described for rapid thermal processing of a wafer using a narrow band beam of electromagnetic radiation generated by a high wattage laser. The beam is directed at the wafer, through a thin absorption film, which absorbs substantially all the energy from the beam, which, in turn, radiates heat to the wafer. Unfortunately, the apparatus described above has some limitations and drawbacks. For example, the thickness of the thin film must be accurately determined. If the thin film is too thin, energy from the beam may be transmitted directly to the wafer, or if the thin film is too thick the film may not heat up fast enough for rapid thermal processing. A film must be used that does not degrade over time, and must not sputter, bubble, or degas when heated, otherwise non-uniform absorption will result. Because of the requirements placed on the thin absorption film, the materials for this film are limited. As a result, the same RTP apparatus may heat wafers differently and unpredictably, which wastes both time and materials.
The present invention provides a system and method for uniformly and controllably heating the active surface of a semiconductor wafer or substrate during processing. The present invention may include, as described in greater detail below, a radiation energy source provided, which is enclosed or substantially surrounded by a reflective/absorptive surface, which both reflects and absorbs the radiation, emitted from the energy source such that the resultant energy output as seen by the wafer is substantially free of non-uniformity. Advantageously, the resultant energy can be uniformly spread over the wafer to heat only the active layer of the wafer surface. Because the resultant energy is uniform over the diameter of the wafer there is no significant heating overlap.
In accordance with the present invention the resultant energy can be provided at a very high intensity such that only a short exposure time is necessary to heat the active layer of the substrate. Thus, the process can be referred to as a xe2x80x9cflashxe2x80x9d anneal process, which can include crystallizing the active layer of the substrate, doping the active layer, or otherwise heat treating the active layer. Optionally, the present invention can provide a continuous heat exposure to allow the bulk of the substrate to be heated.
In one aspect of the invention, a system is provided for rapid thermal processing of a substrate. The system includes a radiation energy source surrounded by a reflector, which causes radiation energy to impinge on a surface of a substrate to heat an active layer of the substrate. The surface of the substrate is impinged on by the radiation energy for a substantially instantaneous reaction time.
In another aspect of the invention, a method for rapid thermal processing of a substrate is provided including providing a chamber including a radiation energy source and a reflector; and focusing radiation energy from the radiation energy source at a first focal point to impinge on a surface of a substrate for a substantially instantaneous time to heat an active layer of the substrate.
In yet another aspect of the present invention, a method is provided for rapid thermal processing of a substrate. The method includes providing a chamber including a radiation energy source and a reflector; raising the power level of the radiation energy source to a peak power level to expose an active layer of a substrate to a first radiation energy for a first time duration; and thereafter maintaining a second power level of the radiation energy source, less than the first power level, to expose a bulk of the substrate to a second radiation energy for a second time duration.
The system and method of the present invention can be used to heat only the active layer of the substrate surface, thus the process is advantageous for implant anneal applications, such as shallow junction, ultra shallow junction, and source drain anneal. The RTP system and method may also be used effectively for thermal donor annihilation, re-crystallization, and impurity doping. Moreover, since the bulk of the semiconductor wafer need not be heated during the heating process, unless desired, the amount of power used by the RTP system can be reduced to less than 50 kWh, preferably, less than about 10 kWh. Similarly, processing times maybe reduced since only the active surface of the wafer is being heated.
These and other features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings.